I went from a 4670k to a 10900k in september when the 3000 series launched, I had the same worry as i knew an AMD cpu was in the horizon but no one knew the performance obviously so i bit the bullet.
I have the same user case as you basically, gaming and just general browsing etc and let me tell you, its a night and day difference. It is surprising with just simple things like opening file explorer and the snappyness of it let alone in gaming!
After watching reviews when the 5000 series, if you are gaming anything higher than 1080p then the difference between AMD and Intel is negligible either way and as you said from the reviews i seen the 10900k generally slightly ahead than the 5900x but again they trade blows dependant on title so it really doesnt matter.
From someone that was in your position only a couple of months ago, you are going to be incredibley pleased and you are going to enjoy it very much! I paired it with a 3090 when i was on a 1060 before so everything has been fantastic for me!